This invention relates to x-ray microscopes and more particularly to a narrow bandpass high resolution x-ray microscope for imaging microscopic structures within biological specimens, the bandpass being in the water window wherein x-rays are absorbed by carbon and not absorbed by water within cells and tissues.
The water window is the narrow x-ray band which lies between the K absorption edge of oxygen and the K absorption edge of carbon, the former being 23.3 angstroms and the latter being 43.7 angstroms. X-Rays of wavelength just below the K absorption edge of oxygen are highly absorbed by water, but at wavelengths just above the 23.3 angstrom K absorption edge, water is quite transparent. Similarly, carbon structures are very absorptive to wavelengths just below the carbon K absorption edge of 43.7 angstroms, but transparent at longer wavelengths. Because of these natural properties of the interactions of x-rays with matter, a microscope designed to produce images using x-rays of wavelength lying within the relatively narrow water window would provide a unique instrument ideally suited for ultra-high resolution studies of proteins, cell nuclei, chromosomes and gene structures, DNA and RNA molecules, mitochondria, viruses, cellular golgi apparatus and other carbon based structures within the aqueous environment of living or freshly killed cells. Such a microscope would take specific advantage of the nature and characteristics of x-ray absorption in the immediate vicinity of the K edges of the dominant components within living cells and tissues. It can thus be utilized for medical and microbiological research into the nature and characteristics of DNA and RNA molecules, genetic structures and investigations of proteins, protein crystals, viruses and a host of other microscopic carbon based structures. The value of a microscope permitting images of the important carbon constitutes of microscopic structures should be of immense value in many biological and medical research areas including DNA and RNA research, genetic research, gene splicing, genetic engineering, cancer and AIDS research.
The prior art x-ray microscopes are broad bandpass systems. Thus, they are not capable of yielding high resolution, high contrast images of carbon structures within living cells since x-ray absorption within the water of the cell degrades the contrast and makes it impossible to obtain quality images of the small carbon based structures. These prior art microscopes have been fabricated based upon grazing incidence systems using the principle of the Kirkpatrick-Baez configuration and the Wolter (Hyperboloid-Ellipsoid) configurations. The single Wolter or crossed Kirkpatrick-Baez systems are typically made to operate at a low grazing angle of incidence, e.g., less than one degree and typically are effective reflectors of x-rays of wavelengths greater than 6 angstroms whether or not they are uncoated or coated with a high-Z diffractor material as gold, platinum or iridium Because they are broad bandpass systems an x-ray microscope of the prior art capable of reflecting radiations as short as 23.3 angstroms will also effectively reflect wavelengths much longer than 43.7 angstroms where carbon becomes transparent. Consequently, the prior art microscopes are not suited for research in the critical and relatively narrow band of the electromagnetic spectrum in which the properties of water and carbon, the components most important to living cells, play the dominant role in governing the achievable spatial resolution and contrast. An imaging microscope capable of having the narrow x-ray bandpass of the water window although invaluable to many biological and medical research areas is not known in the prior art.